Internal combustion engines include one or more pistons interconnected by connecting rods to a crankshaft, and are typically disposed to reciprocate within bores formed in a crankcase, as is known. A typical piston includes a head portion, which at least partially defines a combustion chamber within each bore, and a skirt, which typically includes a pin opening and other support structures for connection to the connecting rod of the engine. In general, a piston is formed to have a generally cupped shape, with the piston head forming the base, and the skirt portion being connected to the base and surrounding an enclosed gallery of the piston. In typical applications, lubrication oil from the engine is provided within the gallery of the piston during operation to convectively cool and lubricate various portions of the piston.
A typical piston head also includes an outer cylindrical wall having one or more circumferentially continuous grooves formed therein. These grooves typically extend parallel to one another and are appropriately sized to accommodate sealing rings therewithin. These sealing rings create sliding seals between each piston and the crankcase bore it is operating within. Typically, the groove located closest to the skirt of the piston accommodates a scrapper ring, which is arranged to scrape oil clinging on the walls of the piston bore during a down-stroke of the piston. Oil that may remain wetting the walls of the bore following the down-stroke of the piston may enter the combustion chamber and combust during operation of the engine.
One known solution for improving the removal of oil found on the bore walls during a down-stroke of the piston can be seen in U.S. Pat. No. 6,557,514, which is incorporated herein in its entirety by reference (hereafter, “the '514 patent”). The '514 patent discloses a piston having an outer wall defined in part by a ring belt and including an oil gallery defined internally to the piston. An oil drainage groove is machined into the outer surface of the ring belt of the cylindrical side wall of the piston head, below two piston ring seal grooves. The oil drainage groove is partially defined by a bottom wall that extends circumferentially about the piston but is interrupted such that oil gathered in the oil groove can drain downwardly back into the crankcase of the engine. An upper wall of the oil drainage groove extends about the circumference of the body of the piston. As disclosed in the '514 patent, the upper ring grooves accommodate piston rings, while the bottom-most groove is free of piston rings and is arranged to collect oil as the piston undergoes a down-stroke.
The oil collection groove disclosed in the '514 patent is at least partially effective in reducing the amount of oil left behind on the cylinder wall after the piston has undergone a down-stroke.
With the foregoing as background, it is sometimes the case that a mature engine design, especially one that is already sold to consumers, is in need of improvements in performance, cost, or sourcing of components, which will render the engine more successful in the marketplace. Such product improvements for engines are especially valuable to an engine manufacturer if reverse compatibility of new components to be used in place of original engine components is preserved. Nevertheless, it has traditionally been the case that engine pistons are not considered as components that may be redesigned mid-stream through the product life cycle of a particular engine.
The unsuitability of engine pistons as components that may be redesigned to fit an existing engine and replace an existing, baseline piston design is because, in large part, design changes made to a piston will often require a cascading series of changes to other engine components. For example, a design update to a piston may cause changes to the weight balancing, performance, and/or any other functional attribute of the piston, which in turn will necessitate changes to the counterweights of the crankshaft, or changes to connecting rods and to engine calibration. Moreover, it is conceivable that engine overhaul service providers may replace some pistons but leave others with less wear or damage alone which would cause serious performance problems if the replacement piston was a different weight as compared to the original piston. Any such changes to the design of engine components renders retrofitting of certain components, such as pistons, effectively unsuitable for current-production engines.